Blood sucking parasitic infestation on animals, especially the infestation of pets by fleas, has been a continued problem in the art. Infestation of dogs and cats with fleas may cause local irritation or annoying scratching. Intense scratching can lead to open wounds that can become infected with bacteria.
Many different types of flea deterring or larvicide or adulticide treatments have been developed in attempts to rid animals of fleas. A variety of products have been marketed for controlling flea infestation in household pets such as dogs, cats, hamsters, etc. Most products contain harsh chemicals that can have serious consequences when used too often or in excess of recommended quantities. Typical of these chemicals are propoxur (o-isopropoxphenyl), methyl carbamate, diazinon, chlorpyrifos, d-limonene, cyano(3-phenoxypheny)methyl 4-chloro-alpha (1-methylethyl)benzeneacetate, pyrethrins, piperonyl butoxide and N-octyl bicycloheptane dicarboximide. Although these chemicals are generally effective against fleas if used carefully, they can often have serious side effects. Flea resistance to these compounds has also been seen in the field. Many products may excessively dry the skin or cause eczema or allergic reactions in some animals. Skin wounds caused by the animal's scratching at fleas can become infected and the infections are often aggravated by these chemicals. Many of these chemicals cannot be applied to the fur of animals, such as cats, that self-groom by licking the skin and fur. Persons applying these flea killing chemicals to animals must often be very careful to avoid excessive contact with them. Those grooming animals are advised to wear rubber gloves to avoid continuous contact with the chemicals. Care must be exercised to keep the chemicals out of the eyes and away from the mucus membranes of both the animal and the person applying them. Breathing vapor from the chemicals over long periods must also be avoided. Many of these chemicals are not rapidly biodegradeable and constitute an environmental hazard if misused. Thus, there is a continuing need for improved and fully effective materials that can be applied to fur bearing animals to eliminate fleas while being environmentally benign, and avoiding deleterious side effects.
1-(4-SF.sub.5 -phenyl)pyrazoles of formula I are known compounds reportedly to be useful as insecticides (see U.S. Pat. No. 5,451,598). They have not been disclosed as useful in controlling ectoparasites, such as flea and tick infestations in animals.
PCT Published Application WO97/12521 discloses ready-to-use solutions for topical application against fleas and ticks containing as active ingredient a compound of the formula 1: ##STR1## wherein Y may be halogen or SF.sub.5, among others, and p may be from 1 to 5. The only active compound specifically exemplified in the claimed ready-to-use solution is the compound fipronil 2: ##STR2##
Fipronil is commercially available in topical formulations against fleas and ticks. It has been known to cause vomition in animals when administered systemically. Topical application of fipronil provides efficacy for not more than three months.
The present inventors have found that certain SF.sub.5 -phenylpyrazoles are highly potent agents against fleas and ticks. More particularly these SF.sub.5 -phenylpyrazoles exhibit higher potency than fipronil against fleas. The SF.sub.5 -phenylpyrazoles may be formulated for systemic administration to provide efficacy against fleas and/or ticks for extended period while avoiding or reducing the potential of vomition and/or other adverse reactions in treated animals.